The segregation of human chromosomes in rodent-human somatic cell hybrids presents a unique opportunity for mapping components of the human genome. We propose to utilize somatic cell hybrids containing one to several human chromosomes to explore cell surface antigens coded for by the human genome which are expressed on the hybrid cell. The immunogenicity of clonally-derived hybrid cells containing different human chromosomes will be checked by generation of antisera within the inbred strain from which the rodent parental cell was derived. The capacity of each human chromosome to code for recognizable cell surface antigens within the inbred rodent system will thus be investigated and correlated with the immunogenetic history of the human parental cell in an attempt to define the minor as well as the major histocompatibility loci of the normal human genome. At the same time we plan to utilize human-murine hybrid cells in tumorgenicity studies. Hybrid cells derived from fusion of human tumorigenic cells with primary mouse cell or with nontumorigenic murine cell lines will be injected into athymic (nude) mice and tumorigenicity of such hybrids determined. Using hybrid cells which possess one or a few human chromosomes we shall determine if a specific human chromosome(s) is necessary for tumorigenic growth of the hybrid cells in the nude mouse. We will also compare cells derived from normal human cells to determine if unique cell surface antigens are present.